Machines such as wheel type loaders includes work implements capable of being moved through a number of positions during a work cycle. Such implements typically include buckets, forks, and other material handling apparatus. The typical work cycle associated with a bucket, for example, includes filling the bucket with material, carrying the material to a dump site, and dumping the material from the bucket.
Machines of this type generally do not include shock-absorbing suspension systems. Thus, as the machine is travelling, the forces exerted on the machine by the terrain cause the machine to pitch and/or bounce which result in considerable operator discomfort and increased wear on the machine.
When the lift cylinders are rigidly maintained in position while the machine is travelling, the bucket and lift arm assembly move in connection with the pitching and bouncing of the machine. The substantial mass of the bucket and lift arm assembly, particularly when the bucket is filled with material, tends to exacerbate the effects of the pitching and bounces.
In an effort to reduce the effects of these forces, hydraulic accumulators have been added to the lift cylinder hydraulic circuit. Such an arrangement is disclosed in U.S. Pat. No. 3,122,246, issued to Freedy et al. on Feb. 25, 1964. This arrangement allows hydraulic fluid to flow from the head end of the lift cylinder to an accumulator and from the rod end of the lift cylinder to a fluid reservoir.
Thus, when the machine is pitching the forces that would otherwise be transferred to the lift arm assembly and bucket are absorbed by the accumulator. In this way, the lift arm assembly and bucket tend to be isolated from the pitching and bouncing of the machine. Since the mass of the lift arm assembly and bucket is not involved in the pitching and bouncing, the effects in the vehicle are lessened.
However, when the machine is loading material into the bucket, substantially all of the forces produced by the drivetrain of the machine should be transferred to the bucket. If the accumulator is connected to the lift cylinder while the machine is loading material in the bucket, much of the force needed to fill the bucket with material will be absorbed by the accumulator. The resulting loss of force applied to the bucket causes reduced loading performance. To address this problem, the Freedy et al patent disclosed a manual switch for opening and closing a valve between the lift cylinders and the accumulator. The manual switch, however, requires operator attention each time the valve is opened or closed.
One effort to provide a system which required less operator intervention, is disclosed in U.S. Pat. No. 5,147,172, issued to Javad Hosseini on Sep. 15, 1992 and assigned to the assignee of the present invention. The Hosseini patent discloses a ride control system which connects and disconnects an accumulator from a lift cylinder hydraulic circuit as a function of machine ground speed. In other words, the system activates the ride control system when ground speed is above a set value and deactivates the ride control system when ground speed is below a second set value.
However, it has been found that different operators have different preferences for the operation of the machine. In other words, some operators prefer better control over implement actuation over a wider speed range than other operators.
The present invention is directed at solving one or more of the problems as set forth above.